Windows 32bit Family XP RTM - 5.1.2600
XP SP1a - 1106
XP SP2 - 2180
Server 2003 RTM - 5.2.3790
Server 2003 SP1 - 1830
Server 2003 SP2 - 3959
Vista RTM - 6000.16386
Server 2008 Beta 3 - 6001.16510
Windows 64bit Family XP 64bit RTM - 5.2.3790.1830
XP 64bit SP2 - 3959
Server 2003 64bit RTM - 5.2.3790.1830
Server 2003 64bit SP2 - 3959
Vista 64bit RTM - 6000.16386
Server 2008 64bit Beta 3 - 6001.16510
It looks like Microsoft are getting ready to release Windows Server 2008 RC0 to the general public soon. A search in Google for "Server 2008 Beta 3" or "Server 2008 RC0" returned the usual links to the Beta 3 download site but had a link title name of "Evaluate the Windows Server 2008 Release Candidate today". While the actual MS site lists the current version as Beta 3, Google Cache has the following updated RC0 page:
Microsoft have also already released RC0 to TAP as noted in Andy Malone's Blog.